Measuring the movement and strength of an infant tongue during sucking on the nipple of a bottle or pacifier presents several challenges including, for example, the limited oral space of the infant available for direct measurement and alteration of motor control feedback mechanisms induced at the tongue interface, the limited amount of space available for instrumentation of the nipple, alterations required for instrumentation of the nipple which could affect natural feeding patterns, and obtaining accurate and precise measurements of tongue contact with the nipple interface. There are two stages of feeding where the tongue is applied to the nipple. During one stage, compression (squeezing) of the nipple by forces exerted on the nipple by the tongue compresses the nipple against the palate. In a nutritive sucking condition, a volume of fluid present in the nipple is pushed out of the nipple and into the oral cavity due to compression of the nipple. In the other stage, with the oral cavity sealed, the jaw and tongue drop down and away from the palate, enlarging the oral cavity and creating negative intra-oral suction. In a nutritive sucking condition, fluid is drawn (sucked) out of the nipple. Both stages are essential to infant feeding.
Adaptations to tongue muscle including decline of or lack of improvement in tongue strength may occur in premature infants who are artificially fed for a period of time. Using animal models, researchers have documented significant negative changes in tongue muscle responsiveness as a result of artificial feeding of newborn rats, which result in long term difficulties with feeding. As many as forty percent of premature infants exhibit both immature and atypical feeding patterns and those requiring prolonged respiratory support and those experiencing delayed oral feeding are most often affected. Because artificial feeding of premature infants may not be avoidable, determining whether tongue force is adequate for safe, efficient oral feeding, and developing interventions that lessen or eliminate any negative impact on the tongue muscle, such as interventions for strengthening the tongue during non-nutritive suck (NNS) and nutritive suck (NS), are necessary. Clinical use of NNS with preterm infants to promote oral feeding is well documented. Indications are that NNS intervention has a positive impact on transition from tube feedings to oral feedings, improves bottle feeding performance and decreases length of stay. Volume intake, number of tube feedings prior to reaching full oral feeds, and impact on growth and weight gain are outcomes that have not been positively associated with NNS, and the impact of NNS on other important oral feeding outcomes is not clear. Current measurement and evaluation methods are lacking and those that currently exist are subjective in nature and provide limited empirical evidence relative to assessment of infant feeding and swallowing.